You can use the Files app Set up file sharing on Mac in the macOS User Guide.
Download the app from the App Store, then open the app and follow the onscreen instructions.
Open Files, tap More Locations (below Locations in the Browse sidebar), then turn on the service.
To view your contents, tap Browse at the bottom of the screen, then tap the name of the storage service below Locations. If you don’t see Locations, tap Browse again at the bottom of the screen.
For information on how to connect external storage devices and SD cards, see Connect external storage devices to iPad.